1. Field of the Invention
The present invention relates generally to a reticle, mask or photomask used in photolithography for the manufacture of semiconductor devices, and more particularly to a reticle with reduced thermally induced distortion.
2. Related Art
In the manufacture of semiconductors using photolithography, a mask or reticle is used to project the image of a circuit pattern onto a photosensitive resist covered wafer. As the feature size of the elements in the circuit pattern become smaller, the need for increased resolution and dimensional accuracy also increase. There have been many advances in improving the mask or reticle used in the photolithographic process. One such improvement is disclosed in U.S. Pat. No. 5,322,748 entitled Photomask And Method Of Manufacturing Thereof Comprising Trapezoidal Shaped Light Blockers Covered By A Transparent Layer, issued to Watakabe et al on Jun. 21, 1994, which is herein incorporated by reference. Therein disclosed is a phase shift mask used to improve resolution of the image projected onto a photosensitive wafer. While such improvements have advanced the state of the art, this invention does not deal with this type of improvement. As the throughput of the tools used to manufacture semiconductor wafers is increased due to the need to increase production, problems may arise. For example, in an effort to decrease the exposure time in a photolithographic process, high energy flux illumination is used. As a result of this increase in intensity or flux, portions of the mask or reticle may absorb sufficient amounts of this energy to create undesirable thermal distortions. These thermal distortions will create errors in the imaging of the pattern contained on the reticle or mask which is projected onto a photosensitive resist covered wafer. Accordingly, lower yields would be expected in the finished semiconductor device, thereby increasing the cost of manufacture. Accordingly, there is a need for a mask or reticle that has reduced thermal distortion which can accommodate the higher energy flux illumination used in an effort to increase productivity, and as the operating resolution diminishes these effects will become more significant.